I am having this problem right now as well.
I was running 1.3.7 bios. I have 2 Quadro NVS 290 PCIE-1X cards.
For the sake of reducing complexity of hte problem, I have only 1 Quadro NVS 290 card inserted. Machine boots, get video out of primary vga (EVEN if it is disabled in win7-- this is odd.. Didn't think that was possible.)
Device manager shows the Quadro NVS 290 working perfectly, BUT i don't have access to any of the displays in the display control panel, it only shows the 1 standard vga. Tried updating the drivers on the RN50 card, the quadro card, no dice.
I updated to the most recent bios (as of 9/21/2010) and still no dice. Windows doesnt report any problems, but I can't use any addin cards. I have also a geforce 8400 PCIE-1X card, same result.
Please help We just ordered a bunch of the cards, replacement drives, etc for these 1950s